1. Field of the Invention
The present invention relates to a multi-scan compatible horizontal synchronizing signal generating system for making a horizontal synchronizing signal compatible with multi-scan by generating a predetermined horizontal deflection frequency in a television receiver, a monitor apparatus or the like.
2. Description of the Related Art
As television horizontal deflection frequency generating system, there have hitherto been known not only the television system such as the standard NTSC system and the PAL system but also an EDTV (Extended Definition TV) system for displaying a non-interlaced image by line-doubling an existing NTSC image and a line-doubling system which might be called a flicker-free system for removing a flicker in the PAL system, for example. Also, broadcasting based on a MUSE (Multiple Sub-Nyquist Sampling Encoding) has already been started. From such background, television receivers corresponding to both systems of the MUSE system and the NTSC system have been known.
Then, the above-mentioned systems have different horizontal deflection frequencies. The standard NTSC system has a horizontal deflection frequency of 15.734 kHz and the PAL system has a horizontal deflection frequency of 15.625 kHz. Moreover, since the EDTV system and the line-doubling system of the line-doubling or field-doubling system based on the NTSC, the PAL including the flicker-free system require a horizontal deflection frequency twice as high as those of the standard NTSC, PAL system, the line-doubling system based on the NTSC system (including the EDTV system) requires a horizontal deflection frequency of twice as high as that of the standard NTSC system, 15.734xc3x972=31.468 kHz. Moreover, the line-doubling system based on the PAL system such as the flicker-free system requires a horizontal deflection frequency twice as high as that of the standard PAL system, 15.625xc3x972=31.25 kHz. Furthermore, the MUSE system requires a horizontal deflection frequency of 33.75 kHz.
As described above, when various kinds of television systems become available, although different systems have different horizontal deflection frequencies, a horizontal deflection frequency generating apparatus should preferably be made common from a manufacturing cost standpoint. It was very difficult to form a horizontal deflection frequency generating circuit which may be made compatible with all of the above-mentioned horizontal deflection frequencies of various kinds of television system.
There have hitherto been known two methods of generating a horizontal deflection frequency in a television receiver compatible with a computer display or a point (fixed) frequency.
Initially, a first method is to generate a sawtooth signal by charging and discharging electric charges of a capacitor. FIG. 1 shows its fundamental system diagram. Reference letter C denotes a capacitor to and from which electric charges are charged and discharged. Current sources I0, I1 to which a current flows may be selected by a switch SW. When the current source I1 is selected, a terminal voltage V increases.
When the terminal voltage V becomes higher than a voltage V1, a comparator 1 connects the switch SW to the opposite side to thereby select the current source I1. As a consequence, the terminal voltage V decreases. When the terminal voltage V becomes less than the voltage V0, a comparator V0 connects the switch SW to the current source I1 side again to thereby select the current source I1. After a series of operations were repeated, the terminal voltage V has a sawtooth wave shown in FIG. 1B. The signal thus generated can be used as a fundamental signal of a horizontal deflection signal.
The sawtooth wave of FIG. 1B generated by the first method shown in FIG. 1 is set to the same frequency as the horizontal deflection frequency or a multiplied frequency. In order to make the first method correspond to the multi-scan, if the current values of the charge and discharge current sources I0, I1 increase, then an oscillation frequency increases. Therefore, if angles at which a sawtooth voltage increases or decreases are changed as shown in FIGS. 2A, 2B, then a fundamental frequency is changed so that the first method can be made corresponding to the multi-scan.
However, according to the first method, a problem of jitter performance cannot be neglected. Since a noise is entered into the current sources I0, I1 due to an action of thermal noise from an element, which may determine the reference potentials V0, V1 and the oscillation frequency, it becomes very difficult to use such sawtooth wave signal as a horizontal deflection signal which may be sensitive to the jitter performance. Therefore, there have been adopted various countermeasures such that the values of the current sources I0, I1 are increased considerably in order to make an apparent noise level become small and the capacitance of the capacitor C should be increased as well in order to prevent the oscillation frequency from increasing. However, as the capacitance of the capacitor C increases, the area of an integrated circuit increases, and a power consumption increases unavoidably. In practical design, it should be executed in such a manner that the capacitance of the capacitor C and the current values of the current sources I0, I1 should be suppressed to be small to the extent that a jitter performance may not be degraded. However, since the capacitance of the capacitor and the current values of the current sources are designed to be as small as possible, in actual trial manufacturing, unavoidably, there invariably arises a problem that a jitter performance cannot be improved as it is expected.
Moreover, the biggest defect of this method is that this method requires an adjustment. The capacitance of the capacitor C and the current values of the reference potentials V0, V1 and the current sources I0, I1 should be constantly fluctuated because their components are assembled as integrated circuits. That is, some integrated circuits have a large capacity but other integrated circuit has a small capacity. Therefore, if the above-mentioned integrated circuits are oscillated according to the first method, then their frequencies are unavoidably fluctuated, and the integrated circuits are caused to output different oscillation frequencies. To solve this problem, when such integrated circuits are designed, it is customary that the oscillation frequencies should be adjusted. Thus, after such integrated circuit is mounted on the computer display or the television receiver, the oscillation frequency should be adjusted, which therefore leads to an increase in the manufacturing cost.
Next, a second method is such one in which an oscillator such as a ceramic is used to generate a clock having a reference oscillation frequency f0 without fluctuations and this clock is counted in descending order such that this clock may become a horizontal deflection frequency. FIG. 3 is a block diagram to which reference will be made in explaining this method. An oscillator 101 which oscillates a reference clock may include a ceramic or crystal piezoelectric transducer member having a high Q (a measure of sharpness of piezoelectric transducer system) as an oscillation element. A clock without fluctuations may be generated from the oscillator 101. When a counter 102 counts this oscillation frequency f0 by a value which results from dividing this oscillation frequency with a horizontal deflection frequency fh in a descending order, there can be generated a horizontal deflection clock. It is natural that this method need not adjust the oscillation frequency.
However, the arrangement of this method cannot be made compatible with multi-scan (synchronizing signal generating system compatible with a variety of frequencies if frequencies fall within a determined frequency range). For this reason, in order to make the second method become compatible with the multi-scan, there are further illustrated decoders 111 to 113, which can be made compatible with three kinds of horizontal deflection frequencies. Therefore, this method needs much more decoders in order to obtain a desired horizontal deflection frequency.
Further, a television horizontal synchronizing signal generating system needs various timing signals, e.g. a clamp pulse timing, a blanking timing, a leading edge timing, a trailing edge timing of H drive for horizontal deflection and the like. FIG. 4 is a timing chart showing leading timing signals. In the sheet of drawing, VIDEO signal denotes an inputted video signal, H-SYNC denotes its horizontal synchronizing signal, H-BLK denotes a blanking signal of a video signal, BGP denotes a burst gate pulse or a clamp timing signal of a video signal, HDV denotes a phase comparator timing signal for establishing a synchronization with the center of the horizontal synchronizing signal H-SYNC, and HDREF denotes a timing signal for establishing a synchronization with a flyback pulse FBP from a deflection-system circuit. An integrated circuit may generate a surface acoustic wave SAW at timing of a timing signal HSTIM, and may generate the timing signal of the horizontal deflection signal H-DRV by slicing the surface acoustic wave with a voltage which results from phase-comparing the flyback pulse FBP and the timing signal HDREF.
In this manner, the horizontal synchronizing signal generating system needs various timing signals. To this end, there are used clock signals having frequencies constant times as high as the horizontal synchronizing signal fh. There is used a pulse 32 times as high as the fh clock as a timing signal as illustrated on the uppermost portion of FIG. 4.
It is to be understood that this timing signal can be varied. In the case of a certain horizontal deflection frequency fh, let it be assumed that the count number of the counter is n0. Then, when a horizontal deflection frequency is fh1, the count number becomes not n0 but n1. The value of the counter in certain timing may be changed to entirely different values as the horizontal deflection frequency is changed. FIG. 5 shows an example thereof. This example shows the timing of a clamp pulse. In video signals 1 and 2 having different frequencies, the video signal 1 has timings of counter values 5, 6, 7 necessary for clamp pulse, and the video signal 2 has a timing of counter values 7, 8, 9 necessary for clamp pulse.
It is an object of this invention to provide a system which can solve a problem in which a horizontal deflection frequency generating system compatible with all horizontal deflection frequencies of various kinds of television systems cannot be formed without difficulty because a lock range is narrowed by using an oscillator such as a ceramic having high Q and a system capable of realizing a low jitter, becoming compatible with a multi-scan deflection, removing an adjustment and which can generate pulses compatible with various timing signals.
Therefore, according to a first of the invention, there is provided a system for generating a horizontal synchronizing signal compatible with multi-scan including a oscillator having a fixed frequency oscillated at a frequency f0 sufficiently higher than a deflection frequency in a multi-scan display, a first counter for counting a clock outputted from the oscillator in descending order wherein an integer which results from rounding a number less than a decimal number obtained by a division of f0÷fh is divided by an integer m less than n to thereby obtain a value k and a time in which the first counter counts the value k is set to one cycle, and a second counter for counting the value k m cycles to form one period, thereby generating the deflection frequency fh and a clock having a frequency multiple times the deflection frequency.
According to a second of the invention, a system for generating a horizontal synchronizing signal compatible with multi-scan according to claim 1, further comprising a third counter in which a value counted in an ascending order can be set freely and wherein in a calculation in which a remainder p is obtained in a calculation of n÷m=k, the value counted in an ascending order is set to p, the third counter counts the value in an ascending order once during the first counter counts the value k, when the counted data becomes larger than m, the first counter set the count value of the next one cycle to k+1, the third counter subtracts m from the counted value and counts the value p in an ascending order with respect to that counted value during the next one cycle, thereby eliminating a deviation of the deflection frequency caused by the remainder p.
Further, according to a third of the invention, in a system for generating a horizontal synchronizing signal compatible with multi-scan, wherein in the system in which the time in which the first counter counts the value k is set to one cycle and the duration in which the first counter repeats m cycles is set to one period, an error of a deflection frequency clock m times as high as the deflection frequency is alleviated by setting an initial value of the third counter to m/2 in the beginning of one period.
Furthermore, according to a fourth invention, the value m is set to power of 2. According to a fifth invention, the system generates a clock having a frequency m times, fixed times, as high as the deflection frequency fh from its inside and generates a variety of timing signals necessary for a system for generating a horizontal synchronizing signal compatible with multi-scan by using such clock.